1. Field of Invention
The present invention relates to a process which allows selective modifications to be carried out on individual, existing, extremely small surface structures having dimensions in the nanometer and atomic range, and to the use of this process for storing information units in the nanometer and subnanometer range and for modifying prestored information units of this type.
2. Description of the Related Art
The controlled manipulation of already existing surface structures in the nanometer range is of particular interest in the area of nanotechnology. A process which allows such manipulations would make it possible, for example, to generate more complicated structures stepwise from simpler structures, for example rotationally symmetrical bumps, as can be produced by voltage pulses using the tunneling microscope, in a multistep process. Such capabilities could in turn form the basis for "nanoengineering", ie. for systematic material processing on a length scale of down to the nanometer and possibly atomic range.
On the other hand, consideration of possible applications of nanostructuring processes for data storage gives rise to the demand for not only the writing of information, but also for the erasure or selective modification of prestored information. It is desirable not only to be able to erase the entire data store, for example by thermal treatment, but also to be able to selectively erase individual information bit by bit and if required to re-write information at the same point.
An interesting perspective arises from the thought that not only one of two (binary) defined states which are clearly differentiable from one another can, if desired, be generated per position (for example "structure present" or "structure absent", corresponding to the numerical values "0" and "1" respectively and thus to an information content of 1 bit per position), but instead, for example, one of three or more defined states (for example "structure absent", "unmodified structure present" or "structure subsequently modified in a defined manner present", corresponding to the numerical values "0", "1" and "2" respectively and thus to an information content of more than 1 bit per position) can be generated.
In the past, various processes have been developed for generating surface structures on a nanometer scale. However, to achieve the abovementioned wishes, it is necessary to be able to modify such structures at any time after generation. It is desirable that a modification of this type can be carried out selectively and in a defined manner. Selectively means that the structure to be modified can be targeted individually and that the modification of a structure has no significant effects on adjacent structures. In a defined manner means that the effect of the modification is known, predictable and reproducible, ie. the structure is converted from a defined initial state to a defined final state.